In recent years, small, thin, and fold-type mobile phone apparatus have become the majority. However, miniaturization and thin modeling has led to decreased mechanical strength and rigidity, and there have been many occurrences of damaging the installation parts. Especially, with the single-board that has key operating sections on the front plane and the installation parts on the rear plane, the stress from key pressing transmits directly to the installation parts, and there is a high likelihood of damaging the installation parts. Moreover, the configuration makes it difficult to take measures when the problem of damage arises. Furthermore, the spread of e-mail functions has led to the enlargement of main display sections and the mounting of sub display sections that can be used when the apparatus is closed, and as a result, the weight of the upper chassis of a fold mobile phone apparatus has increased, and the upper chassis and the lower chassis tend to have a poor weight balance.
FIG. 1 is a sectional diagram showing a part of a configuration of a conventional fold mobile phone apparatus. Control circuit 23 and radio circuit 24 are formed on the side of the opposite plane from the operating plane of key circuit board 25, and the installation parts of key circuit board 25, control circuit 23, and radio circuit 24 are supported by means of lower rear case rib 27 formed in lower rear case 8.
As to the operation of key pressing, when key sheet 3 is pressed in the direction of the arrow, the stress from the operating section side of key circuit board 25 transmits to the installation parts on the opposite plane side from the operating section side. Next, this stress is received in lower rear case rib 27 formed in lower rear case 8. Moreover, this stress is received in battery 9 attached to lower rear case 8. Especially, in case the edge portions of the installation parts are situated right underneath the keys, little force of key pressing causes substantial stress to the solder joint portion of the installation parts, and the likelihood of damaging the solder joint portion is high.
Moreover, conventional fold mobile phone apparatus have the installation parts on the side of the opposite plane from the operating side of a key circuit board, and the likelihood of damaging the installation parts by key pressing, bending, and twisting is high. Moreover, a further problem is that miniaturization and thin modeling make the likelihood even higher.
Furthermore, since parts are implemented on the opposite plane side from the operating section side of the key circuit board, when development to new models is considered, miniaturizing a circuit board along with miniaturization of installation parts naturally miniaturizes the operating part as well, thereby leading to the problem of poor operationality.